In the offshore industry there is a need for underwater pipelines. These underwater pipelines may be provided by joining pipe sections together in a substantially vertical position to form a pipeline which is lowered from a vessel to an underwater bottom, for instance the bottom of the sea. In such pipe-laying method, which is commonly referred to as a J-lay method a plurality of pipe sections welded to one another, together forming a part of the pipeline, hang down from a vessel in a substantially vertical direction, where an upper end of the most recently joined pipe section is to be welded to a lower end of a new pipe section being lined up above said upper end.
The new pipe sections to be joined to the catenary of pipe section hanging off the vessel may be in the range of 24 to 120 meters. The joining of the new section requires an installation to hold the pipe section during the welding and to lower the connected pipe section to make the joining of a further pipe sections possible.
This installation, in the J-lay method typically a J-lay tower has large dimensions and typically requires a considerable amount of deck space. Not all vessels have this space available and other equipment has to be omitted in the case a pipe-laying installation, for instance a J-lay tower is required, in order to have enough deck space available for placing such installation.
Furthermore, the required position of the pipe-laying installation, for instance at the bow or stern of the vessel, may also be a preferred position for other vessel equipment such as cranes. In such case it may be desirable to have both the pipe-laying installation and the crane at substantially the same position on the deck, which is generally only possible by exchanging the pipe-laying installation and the crane when one of both is required. The other installation has to be stored temporarily elsewhere, for instance on the deck of the vessel.